Code signal blanking apparatus

Abstract

A code signal blanking apparatus comprising a switching means operative during a given period of a vertical blanking period of a television signal and a reference level setting means for producing an output of the reference level during said given period when the switching circuit is operative. A code signal is blanked by keeping a video signal level of the television signal at the reference level during said given period of the vertical blanking period of the television signal.

We claim: 
     
       1. A code signal blanking apparatus which comprises: a means for receiving a television signal with a code signal superposed thereon during a vertical blanking period;   a sync separator means for producing horizontal and vertical synchronizing signals from said television signal;   a pulse generating means for producing a code signal blanking pulse in response to said horizontal and vertical synchronizing signals;   a switching transistor means adapted to receive the television signal;   an output terminal for outputting the television signal through said switching means; and   a gate means responsive to said horizontal synchronizing signal and said code signal blanking pulse for operating said switching means to supply a reference level to said output terminal through said switching means during a given period within the vertical blanking period, thereby blanking the code signal from the television signal.   
     
     
       2. A code signal blanking apparatus as claimed in claim 1, wherein said given period of the vertical blanking period is selected as a part of a horizontal synchronizing signal period of said vertical blanking period. 
     
     
       3. A code signal blanking apparatus as claimed in claim 1, wherein said reference level is selected as a ground level. 
     
     
       4. A code signal blanking apparatus as claimed in claim 1, wherein said reference level is selected as a pedestal level of said television signal. 
     
     
       5. A code signal blanking apparatus as claimed in claim 1, which further comprises a means for producing a horizontal and a vertical synchronizing signal from said television signal and a pulse generating means for producing a code signal blanking pulse in response to said horizontal or vertical synchronizing signal, and wherein said actuating means includes an AND gate which is responsive to said horizontal synchronizing signal and said code signal blanking pulse. 
     
     
       6. A code signal blanking apparatus as claimed in claim 5, wherein said pulse generating means includes a binary counter and a flip-flop circuit, said counter being adapted to count horizontal synchronizing signals and to be reset by a vertical synchronizing signal; and said flip-flop circuit being adapted to be set by an output of said counter. 
     
     
       7. A code signal blanking apparatus as claimed in claim 5, wherein said pulse generating means includes a one-shot multivibrator, said one-shot multivibrator being triggered by a vertical synchronizing signal. 
     
     
       8. A code signal blanking apparatus as claimed in claim 5, which further comprises a means for producing a mode signal which is high when the television signal is a pay-TV signal, said mode signal being supplied to said AND gate. 
     
     
       9. A code signal blanking apparatus as claimed in claim 1, wherein said switching means is comprised of an emitter-follower type transistor circuit, which is connected to a voltage divider circuit for supplying a pedestal level of the television signal.